Preventive effects and mechanism of heat acclimation on high altitude cerebral edema in rats

Objective To investigate the effects and mechanism of heat acclimation (HA) on rats with high altitude cerebral edema. Methods Adult male SD rats were randomly divided into normal control group (C group), hypoxia group (H group, 7 600 m, 1 d), HA group (34 ℃, 30 d) and hypoxia+HA group (HHA group). All rats were sacrificed after the treatment, and then brain water content, pathological changes (HE staining), neuronal degeneration (Fluoro-Jade B staining) and ultrastructure changes (transmission electron microscopy) were measured and observed. Blood samples were harvested to make blood routine test, blood gas and oxygen dissociation curves. The content of MDA and protein levels of HSP70 and AQP4 in brain tissues were detected. Results Compared with group C (4.50±0.07), the wet to dry weight ratio of brain tissue was significantly increased in group H (4.62±0.08, P < 0.05), meanwhile, that in the HHA group (4.52±0.06) was significantly lower than that of the H group (P < 0.05). In pathological observation, swollen cells, rarefaction cytoplasm, uneven distribution of chromatin and nuclear pyknosis, rupture, dissolved, obvious vacuolation, and aggravated neuronal degeneration were seen in the group H. While in the HHA group, the injury, apoptosis and neuronal degeneration were attenuated. When compared with the values in the group C, hemoglobin level, erythrocyte count, hematocrit, and neutrophil percentage were significantly increased (P < 0.05), and SaO2 and PaO2 was significantly reduced (P < 0.05) in group H. HHA group had further increased hemoglobin level, erythrocyte count and hematocrit (P < 0.05), decreased percentage of neutrophils, and reduced SaO2 and PaO2 in comparison with group H (P < 0.05). Oxygen dissociation curve was shifted to right in the group H compared with group C, and that of the HHA group was further shifted right than that of the group H. In addition, compared with group C, MDA content and AQP4 protein level were significantly increased in group H (P < 0.05), and in group HHA, those were further decreased (P < 0.05), while HSP70 protein was significantly increased (P < 0.05). Conclusion HA exerts effective protection on brain edema caused by hypoxia in rats, which may due to its increasing oxygen supply, reducing oxidative stress, and improve cell damage.